The present invention relates to the concentration of particles in microfluidic devices, particularly to the use of dielectrophoresis to collect or concentrate the particles, and more particularly to the use of dielectrophoresis to collect particles under the conditions of electrokinetically-driven flow.
Microfluidic devices are most useful when operating with small sample volumes. Small sample volumes result in increased reaction times and reduced reagent use which means significantly reduced costs for the multitude of tests that one desires to conduct on any given sample. Dielectrophoretic concentration of the samples is a useful method for achieving these goals. Dielectrohporesis is attractive on the microfluidic scale because the forces become significant and useful at dimensions of less than 1 mm. Electrokinetic/electroosmotic flow is also useful in these devices because it obviates the need for micropumps and microvalves.
The present invention involves the combination of dielectrophoresis (DEP) and electrokinetic/electroosmotic flow. Such combination would not normally be an obvious choice since one might think that the two electric fields and their associated double charge layers may interfere with each other. Also, dielectrophoresis collection works best in the slow boundary-layer flow normally associated with pressure-driven flow. However, by the present invention, it has been found that particles can still collect even in the more uniform flow field associated with electroosmotic flow. The 5-10 mm double charge layer associated with establishing electroosmotic flow does not interfere, or be interfered with, by the DEP field in a significant way.
It is an object of the present invention to collect particles in a microfluidic channel using dielectrophoresis.
A further object of the invention is to provide for dielectriphoretic concentration of particles under electrokinetic flow.
Another object of the invention is to use delectrophoresis to collect particles under the conditions of electrokinetically-driven flow.
Another object of the invention is to use a combination of dielectrophoresis and electrokinetic/electroosmotic flow for the collection of particles in a microfluidic device.
Another object of the invention is to provide a microfluidic device capable on dielectrophoretic concentration of particles under electrokinetic flow.
Other objects and advantages of the present inventions will become apparent from the following description and accompanying drawing. Basically the present invention involves a method and apparatus for collecting or concentrating particles in a microfluidic channel using dielectrophoresis under conditions of electrokinetically-driven flow. This is accomplished by interdigitated electrodes patterned on the inner surface of a microfluidic channel, preferable formed of glass, applying a DC voltage across the ends of the channel to initiate an electrokinetic/electroosmotic flow field, and applying an AC voltage across the interdigitated electrodes to set up a non-uniform electric field capable of trapping particles using the dielectrophortic force. The trapped particles are released upon removal of the voltage to the electrodes.